The prosecutor in Oscar Pistorius’ murder trial on Thursday spent a second day attacking the credibility of a defense witness who was trying to show that the athlete killed his girlfriend by mistake.

Roger Dixon was called by the defense to support Pistorius’ story that he killed girlfriend Reeva Steenkamp, 29, by accident, thinking she was an intruder behind the bathroom door in his Pretoria home who was about to attack him.

Continuing his tough cross-examination on the trial’s 25th day, prosecutor Gerrie Nel said Dixon had no expertise in the subjects he was testifying about and had been careless in his preparation for the trial.

At one point, Nel singled out a photo the defense had taken that was meant to demonstrate what Pistorius’ neighbors would have seen when looking into the Blade Runner’s bathroom window shortly after the shooting on Valentine’s Day 2013.

The prosecutor criticized Dixon, a geologist, for not using the exact height of double-amputee Pistorius, 27, when he was standing on his stumps.

“Why did you not make sure that the person is the exact height as Mr. Pistorius? Why?” he asked Dixon.

“The man’s height is something I overlooked and omitted,” Dixon replied when questioned why his measurements were around 8 inches off.

The ex-cop said he was not trying to “mislead” the court.

His earlier testimony touched on ballistics, gunshot wounds, pathology and blood spatter, and he also said he was involved in audio and visual tests — even though he conceded he is not an expert in any of those areas.

Dixon told the court he does not own a TV or radio, didn’t read newspapers and that he had not been following the case.

But he is active on Facebook, where he posted a self-pitying message after he was widely ridiculed for his earlier testimony.

“Third day in court today. Let’s see how much of my credibility, integrity and professional reputation is destroyed,” he wrote.

Prosecutors charged that Pistorius killed Steenkamp after a fight. The trial has been adjourned until May 5.

Judge Thokozile Masipa will ultimately deliver a verdict. Pistorius faces 25 years to life in prison if convicted on a charge of premeditated murder.